1. Field of the Invention
The present invention relates to a control apparatus for a parallel hybrid vehicle, and in particular, to a control apparatus for a parallel hybrid vehicle that carries out limiting control of the engine speed according to conditions.
2. Description of the Related Art
Recently, the development of electric vehicles has been progressing with the aim of reducing exhaust gas emissions into the atmosphere. However, in the electric vehicle that is being driven as an automobile using only an electric motor actuated by electric energy, the cruising distance is limited by the charge of the battery that stores the electric energy. Contrariwise, if a sufficient cruising distance is to be attained, a huge number of batteries is necessary, and the driving performance of the automobile noticeably deteriorates.
Thus, by using in parallel a combustion engine with the above motor, the size of the battery, which is the power source of the motor, can be reduced, and the development of hybrid vehicles having both cruising distance and driving performance can be developed.
A parallel hybrid vehicle, which is one type of hybrid vehicle, decreases exhaust gas emissions and improves fuel consumption while maintaining the driving performance by carrying out driving by using in parallel one drive from an electric motor and another drive from a combustion engine depending on the driving conditions.
That is, in a parallel hybrid vehicle, the motor is controlled so that the engine is driven only in its range of high efficiency, for example, providing assistance to the engine, etc., during departure and acceleration, thus improving fuel consumption.
In addition, while breaking the vehicle, the motor operates as an electrical generator, and by charging the battery by converting the kinetic energy of a drive wheel to electrical output, fuel consumption is further improved.
However, the motor and the battery are connected through a contactor, and this contactor is ON/OFF controlled by being linked with the ignition switch. That is, during non-driving time, when the ignition is OFF, the contactor is OFF.
In addition, the counter-electromotive force (regenerative voltage) is proportional to the speed of the motor (engine), and is controlled so that even if the motor rotation speed moves into the high range, the counter-electromotive force is controlled so as not to exceed the voltage of the battery (weak magnetic field control). This decreases the apparent torque constant of the motor and decreases the counter-electromotive force by outputting a specified switching waveform.
However, when the ignition is turned OFF during traveling when the motor (engine) is in the high rotation range, the contactor, which is linked thereto, turns ON. When this type of operation occurs, because the above-described weak magnetic field control cannot be generated, the counter-electromotive force of the motor increases and exceeds the withstanding voltage of the inverter. There is the concern that withstanding voltage failure of the inverter will occur as a result of this type of counter-electromotive force produced by the motor being applied only to the inverter because the contactor is in an OFF state.
In consideration of the above-described problem, it is an object of the present invention to provide a control device for a hybrid vehicle, which is, even when an operation occurs that does not occur in normal driving, capable of avoiding component failure due to this type of operation, and capable of continuing smooth driving.
In order to achieve the above-described object, according to a first aspect of the present invention, a control device for a hybrid vehicle provides a combustion engine 1 that outputs propulsive force to the vehicle, an electric motor 2 that supplements the output of the engine, a storage device (the battery in the embodiment) that is charged by the electricity generated by the regeneration of the motor, a contactor (the precharge contactor 10 and the main contactor 11 in the embodiments) that connects the motor and the storage device, and an inverter (the power drive unit 7 in the embodiments) provided between the motor and the contactor, wherein, in the case that the ignition is turned ON again after the contactor has been turned OFF due to turning OFF the ignition while the rotation of the motor is high, the rotation speed of the engine is limited to the rotation speed (an engine rotation speed xe2x89xa65500 rpm in the embodiments) where the voltage generated by the regeneration of the motor is equal to or less than the withstanding voltage of the inverter.
In this manner, the engine speed is limited, and by limiting the voltage generated by the regeneration of the motor so as to be equal to or less than the withstanding voltage of the inverter, the inverter (power drive unit 7 in the embodiments) can be protected.
In addition, according to a second aspect of the present invention, the control device of the hybrid vehicle turns the contactor ON and subsequently releases the limitation on the rotation speed of the engine when the voltage difference between the voltage generated by the regeneration of the motor and the voltage of the storage device is within specified values (an engine rotation speed xe2x89xa63300 rpm in the embodiments).
In the case that the voltage difference between the voltage generated by regeneration of the motor and the voltage of the storage device is within specified values, control that turns ON the contactor that is in the OFF state is carried out. In addition, when the contactor is turned ON and a normal state is restored, the limit on the engine speed is released, and the upper limit of the engine speed is set to the rotation speed (7,000 rpm in the embodiments) used during normal driving.
Thereby, normal driving using the motor and engine in parallel can be restored.